Evaluation of Hydrologic Response to Design Precipitations and Land Use/Land Cover Change in an Ungauged Tropical Rainforest Catchment, Southwest Nigeria

This study evaluated Opa catchment’s hydrologic response to design precipitations and land use/land cover change. The study involved hydrologic model building, which consisted of basin characteristics’ extraction, meteorological model and control specifications. The basin characteristics were extracted using Hydrologic Engineering Centre-Geospatial Hydrologic Modelling System (HEC-GeoHMS) extension in ArcGIS 10.0. The meteorological parameters for the model were obtained by using a design rainfall after the frequency analysis of twenty one year annual maximum historical rainfall data based on Log-Pearson type III probability distribution. The 2, 5, 10, 25, 50, 100 and 200 years return periods were analyzed out of which 2, 25, 50 and 100 return periods were selected for flood discharge and volume simulation by the model. The model was calibrated and validated using known rainfall and discharge values in the catchment before it was transferred to the whole catchment. The model was evaluated using Nash-Sutcliffe efficiency (NSE) statistics and index of agreement. The study concluded that hydrologic response to design precipitation and land use/land cover is very significant (P<0.05) and that rainfall-runoff could be modelled for ungauged watersheds using available datasets coupled with GIS techniques in order to sustainably manage the watershed and mitigate flood disasters.